Grinding rollers, such as are used in flour milling for example, require constant monitoring. For example, it can happen that a so-called dry run occasionally occurs in which adjacent grinding rollers touch each other and the drive power of the motor is converted in an uncontrolled manner into heat. If this state lasts for too long, the temperature of the grinding roller may increase to a critical range and possibly cause a fire.
To prevent this, it is already known to monitor the temperature of a grinding roller with the aid of one or more sensors and to output an alarm when a possible ignition temperature is reached. For this purpose, optical systems are often used for detecting the circumferential surface of the grinding roller. However, a problem with this is that these optical systems are located in the product space through which the grindable material also flows. For this reason, such optical systems are extremely susceptible to soiling.
It is known from DE 102 26 411 A1 to measure the temperature of the circumferential surface of a grinding roller with the aid of temperature sensors in a contact-free manner. On account of the distance between the sensor and the circumferential surface of the grinding roller, the actual temperature of the circumferential surface can in part differ considerably from the measured temperature. These deviations then have to be taken into consideration in the evaluation based on purely experimental values, which is long-winded and also prone to error. Moreover, DE 198 19 614 A1 discloses temperature sensors arranged at a distance from the grinding rollers.
It is likewise important to monitor the wear of the rollers. For this purpose, DE 42 22 085 A1 discloses devices for measuring the surface condition of a grinding roller. However, these devices are likewise arranged outside the circumferential surface of the grinding roller and therefore have the disadvantages already described above.
A device and a method are likewise known with which wear can be measured on corrugated rollers. However, the measurement is possible only when the grinding rollers have been stopped. Although this measurement is precise, the grinding installation always has to be brought to a standstill for this purpose.
Furthermore, pressure sensors are also known with which the contact pressure between two adjacent grinding rollers can be measured. Moreover, vibration sensors for grinding rollers are known, for example from WO 2007/025395 A1. All of these sensors are likewise arranged outside the grinding rollers.